Field of the Invention
The disclosed and claimed concept relates to can ends and, more particularly, to can ends made from a sheet material having a reduced base gage and/or a reduced final thickness relative to known can ends. The disclosed concept also relates to tooling and associated methods for providing such can ends.
Background Information
Metallic containers (e.g., cans) are structured to hold products such as, but not limited to, food and beverages. Generally, a metallic container includes a can body and a can end. The can body, in an exemplary embodiment, includes a base and a depending sidewall. The can body defines a generally enclosed space that is open at one end. The can body is filled with product and the can end is then coupled to the can body at the open end. The container is then placed in an oven and heated to cook the product and/or sterilize the product. The heating and subsequent cooling of the container, and food, causes pressure changes. That is, as the food is heated, the pressure inside the container increases. This pressure is identified as an “internal” or “positive” pressure. Containers are structured to resist deformation due to the internal pressure. In an exemplary embodiment, the heating of the container, and food, is performed by pressurized steam. The pressurized steam applies pressure to the outer side of the container. Pressure on the outer side of the container is “external” or “reverse” pressure. Containers are not always structured to resist deformation due to external pressure. Thus, if the metal of either, or both, the can body and/or the can end is weak, the can body and/or the can end will deform due to pressure changes and the container will be defective.
A “can end,” as used herein, is the element coupled to a can body to form a container. The “can end” includes a tab or similar device structured to open the container. As discussed below, “can end” is, typically, formed from a “shell.” That is, a shell is formed from a generally planar blank cut from sheet material. The blank is formed to include an annular countersink, a chuck wall, and other constructs. The concept disclosed and claimed below are discussed as part of a “can end.” It is understood, however, that the disclosed and claimed concept can be formed while the blank is still a “shell” as opposed to a “can end.” That is, while the following discussion uses the term, “can end,” the discussion is also applicable to “shells.”
A container is exposed to pressures during processing. For example, some food items are cooked and/or sterilized while in the container. Such a container is exposed to both internal pressure, also identified herein as “buckle” or “buckle pressure,” as well as external pressure, also identified herein as “reverse buckle” or “reverse buckle pressure.” A container, that is the can body and the can end, must have the strength to resist deformation due to buckle pressure and/or reverse buckle pressure.
Generally, the strength of the container is related to the thickness of the metal from which the can body and the can end is formed, as well as, the shape of these elements. This application primarily addresses the can ends rather than the can bodies. The can ends are either a “sanitary” can end or an “easy open” end. As used herein, a “sanitary” end is a can end that does not have a tab or score profile to open and would have to be opened by use of a can opener or other device. As used herein, an “easy open” can end includes a tear panel and a tab. The tear panel is defined by a score profile, or scoreline, on the exterior surface (identified herein as the “public side”) of the can end. The tab is attached (e.g., without limitation, riveted) adjacent the tear panel. The pull tab is structured to be lifted and/or pulled to sever the scoreline and deflect and/or remove the severable panel, thereby creating an opening for dispensing the contents of the container. The following addresses an “easy open” can end but is also applicable to a “sanitary” can end. That is, a “sanitary”can end is produced in a similar manner, and coupled to a can body in a similar manner. Thus, as used herein, a can end is further defined as including constructs that are used for both “sanitary” can ends and “easy open” ends.
When the can end is made, it originates as a blank, which is cut from a sheet metal product (e.g., without limitation, sheet aluminum; sheet steel). In an exemplary embodiment, the blank is then formed into a “shell” in a shell press. As used herein, a “shell” is a construct that started as a generally planar blank and which has been subjected to forming operations other than rivet forming and tab staking. The shell press includes a number of tool stations where each station performs a forming operation (or which may include a null station that does not perform a forming operation). The blank moves through successive stations and is formed into the “shell.” A shell is, in an exemplary embodiment, a “sanitary” can end that is structured to be coupled to a can body.
For an “easy open” end, a shell is further conveyed to a conversion press, which also has a number of successive tool stations. As the shell advances from one tool station to the next, conversion operations such as, for example and without limitation, rivet forming, paneling, scoring, embossing, and tab staking, are performed until the shell is fully converted into the desired can end and is discharged from the press. Thus, as used herein, a “can end” includes a “shell” as well as a construct including a tab and a score line.
In the can making industry, large volumes of metal are required in order to manufacture a considerable number of cans. Generally, steel cans are made from sheet material having a base gauge, or an original thickness (as used herein, the terms are equivalent to each other), of between 0.0050 inch to 0.0096 inch. The required original thickness of the material is determined by a variety of factors such as, but not limited to, the dimensions of the finished can, the temperature to which the can (and contents) are exposed during processing, the nature of the contents to be placed in the cans, as well as other factors. The original thickness of the material for each specific type, model, and/or style of can and/or can end is, as used herein, the “established thickness.”
That is, for example, the steel used for a common 18.6 oz. soup can has an established thickness of 0.0090 inch. The can end/container formed from steel with this established thickness is structured to withstand a buckle pressure of 34.8 psi and a reverse buckle pressure of 33.0 psi.
An ongoing objective in the industry is to reduce the amount of metal that is consumed. Efforts are constantly being made, therefore, to reduce the thickness or gauge (sometimes referred to as “down-gauging”) of the stock material from which can ends, tabs, and can bodies are made. Alternatively, the material can be thinned from the base gauge to have a thinner, or partially thinner, final thickness that is less than the base gauge. However, as less material (e.g., thinner gauge) is used, problems arise that require the development of unique solutions. As noted above, a common problem associated with can ends for food cans is that they are subject to pressure changes associated with processing the food product within the can. When the base gauge of the metal is too thin, the can end deforms. This is a problem.
One solution to the problems associated with using thin metal is to provide strengthening constructs in the can end. Strengthening constructs include, but are not limited to, recessed or protruding panels that add rigidity to the generally planar can ends. The strengthening constructs are, in an exemplary embodiment, created by forming the panels in the body of the can end. The can end includes other, similar constructs such as recesses for the tab. As noted above, however, the can end and the strengthening constructs are, in an exemplary embodiment, structured to resist internal pressure.
There is, therefore, a need for a can end having a shape that resists deformation even when the can end is made from a down-gauged, i.e., thinner, metal. There is a further need for a can end having a shape that resists deformation from external or reverse pressure.